Xerographic developing apparatus



Dec. 20, 1960 R. E. HAYFORD ET AL 2,965,069

XEROGRAPHIC DEVELOPING APPARATUS Filed April 1, 1958 2 Sheets-Sheet 1 W Y I F/GZ 44 45 43 3 POWDER POWDER c| ou0 CLOUD Q GENERATOR CHARGlNG l! l 1 .ill g lo INVENTOR. A Richard E. Hayford Y Carl K iser ATTORNEY Dec. 20, 1960 R. E. HAYFORD ET AL 2,965,059

XEROGRAPHIC DEVELOPING APPARATUS Filed April 1, 1958 2 Sheets-Sheet 2 5 H 5W Q I 4' I {I l V W INVENTOR. & \12 11 Richard E. Hayford qZ/ 1 7 )Vfl\ BY Carl B. Kaiser ATTORNEY XEROGRAPHIC DEVELOPING APPARATUS Richard E. Hayford, Pittsford, and Carl B. Kaiser, Rochester, N.Y., assignors to Haloid Xerox Inc., Rochester,

N.Y., a corporation of New York Filed Apr. 1, 1958, Ser. No. 725,558

'13 Claims. (Cl. 118-637) This invention relates to the field of xerography and in particular to an improved device for use in the development of xerographic images.

In the art of xerography an electrostatic latent image is formed on an insulating surface, such as, for example, a photoconductive insulating layer or electrophotographic surface by the combined action of an electric field applied through a photoconductive material and action of light or suitable activating radiation on the photoconductive material to cause selective conductivity in accordance with the pattern of radiation to which the material is exposed. The result of this combined exposure and field is to form a pattern of electric charge on the photoconductive layer that is known in the art as an electrostatic latent image which is capable of utilization, for example, by deposition thereon of finely divided material, such deposition being known in the art as development.

It has been found by others in the art of xerography, as disclosed in Landrigan Patent 2,725,304 and Hayford Patents 2,808,023 and 2,817,598, that an electrostatic latent image can be developed very satisfactorily by presenting to the image surface a cloud of charged powder particles with a conductive surface or' development electrode positioned closely adjacent to the image surface, preferably at a distance therefrom in the orderof about to of an inch or in some instances even closer than inch. It has also been found by others in the art of xerography that one effective way of preparing a cloud of substantially uniformly charged particles is to form a powder cloud in a suitable cloud generator and to pass the cloud under conditions of turbulence through a restricted opening, such as, for example, a Capillary tube.

Basic to the use of the development electrode is the desire to reproduce copies of the original image of high quality and without distortion. Electrostatic lines of force exist between the electrostatic charges on the photoconductive insulating layer and areas of different charge potential. When large areas carrying electrostatic charges exist, the lines of force which are present due to charges in the central area of the large area tend to run inward through the photoconductive insulating layer to the conductive backing member which is the nearest surface carrying a different potential. Lines of force runriing from electrostatic charges near the external boundaries of this large area will tend to extend outward and around the outside border of the large area at which point their paths will extend inward through the photoconductive insulating layer tothe conductive backing member. Development of such an electrostatic latent image creates deposition which relates to the paths taken by the electrostatic lines of force or development of the electrostatic fields. Therefore, development of a large area as has just been described tends to reproduce copies" with hollow centers and emphasized edges. To prevent such 'development a surface ispositioned at a slight dis; tance from the photoconductive insulating layer during 2,965,069 Patented Dec. 20, 1960 development. This surface, the development electrode, is composed of a conductive material and, in the case of positive-to-positive reproduction, is usually maintained at about the same potential as the lowest charge on the photoconductive layer; whereas, in negative-to-positive reproduction, is usually maintained at a potential equal tothe highest charge on the photoconductive layer. In this manner, a surface is formed that causes an increase in the lines of force extending outwardly from the plate member, thereby creating electrostatic fields which when developed produces distortion-free and fringe-free high quality copy.

In xerographic development according to these methods there are many inherent problems caused, among other things, by the need for working in an extremely confined space and with extremely fine tolerances, this need being brought about by the narrow space between the image surface and the development electrode. For example, the usual development of a xerographic image involves uniform deposition of powder particles or other finely divided particulate material, across an area of normal picture size which may, for example, be an area whose smallest dimension is several inches or an area whose smallest dimension is a foot or more. The introduction of a cloud uniformly across this entire area in a development space in the order of to /io0 inch thick has obviously presented many serious problems.

I over an area that should be dark, the leading edge of the dark area is not always properly developed. Frequently, on the developed image the dark area appears to be torn so that a white background shows through. Because of this appearance the fiaw is referred to as tearing.

Another difliculty occurs when the powder cloud travels over a large, dark area and then over a large area that should remain white. Although the white area is void of charge, it does not always remain free of powder. Developer particles may deposit in streaks through this area in amounts roughly proportional to the length of the dark area that immediately precedes the white area. This difiiculty is termed streaking." Still another difficulty is that developed images are not always uniformly developed end-to-end nor does extending the development time remedy this defect as, apparently, part of the charge in the image areas at one end of the plate are erased in the development process. Another difficulty encountered is that powder particles, striking the surface of the xerographic plate as a result of mechanical forces, will not only adhere to the plate regardless of the charge on the plate, but the powder particles will also abrade the surface of the plate thereby reducing the life of the xerographic plate in terms of the number of quality reproductions that can be made by the plate.

It is therefore an object of the invention to improve xerographic developing apparatus to attain a uniformly distributed fiow of powder particles carried by an air stream over a moving fiat electrophotographic plate surface in a manner free from localized concentrations or powder-starved zones or streaks, and free from agglomerations of powder particles. Another object of the invention is to improve xerographic developing apparatus for reproducing copies of the original image of high quality and without distor-:

tion.

In the drawings:

Fig. l is a side elevationv view of the xerographic developingapparatusof the invention positioned in the development station ofr a xerographic machine, associated elements being illustrated schematically. r

' Fig. 2 is a plan view of the developing apparatus.

Fig. 3 is a bottom view of'the developing apparatus.

Fig. 6 is an enlarged detail view of a section of the V deflector plate mechanism of the developing apparatus.-

Fig. 1 shows the developing apparatus and related elements with a xerographic plate 10 in position for development. The xerographic plate, which forms no part of the subject invention, consists of a photoconductive insulating layer coated on'a conductive backing, and is supported on carrier .block 11 which in turn rests on drive rolls 12 for movement past the developing apparatus. The developing apparatus is mounted to maintain a uniform close spacing between its lower surface and that of the xerographic plate whereby to form a development zone 13. I

The developing apparatus, generally made of metal or other conductive material, is essentially a manifold or manifold system which contains an entrance slot, through which a stream of fine, electrostatically charged develop-' ment powder particles suspended in fluid is directed into the development zone in substantially laminar, parallel flow to the xerographic plate, and which also contains an exhaust slot through which any excess powder particles are removed from the development zone.

In the embodiment disclosed, the developing apparatus includes a development plate or electrode plate, generally designated 15, consisting of plate 16 having'a deflector plate 17. fastened by screws 18 in the step undercut portion 19 of the plate, and a'flanged riser block 20 attached by means of screws 21 to the top of plate 16.

The plate 16 contains an entrance slot 23 through which a stream of fine, electrostatically charged development powder particles suspended in fluid, commonly called a powder cloud, is directed into the development zone 13. The wal's of the slot 23 are formed by the beveled surface of the undercut portion 19 of the plate 16 and the deflector plate 17, the tapered portion of the deflector plate'and the beveled surface of undercut portion 19 being formed at an acute angle to the horizontal. Preferably this angle should approach zero, but as a practical matter it is usually on the order of from 2 to 5 because the deflector plate must be made of suflicient thickness to minimize excessive Wear. As illustrated in Figs. 3 and 5, the entrance slot extends transversely of the pate 16 but terminates inside the margins of the plate so that the powder cloud is retained within the development zone, the plate 16 being wide enough, so that the entrance slot 23 is substantially the full width of the xerographic plate 10.

Formed in the bottom of the plate 16, as shown in Figs. 3 and 4, is a lateral groove 24 positioned in front of the slot 23 and extending parallel thereto. Q

A pair of channels 25 and 26 are formed in the plate 16 at right angles to the bottom of the plate, the bottom surface of the dividing wall 27 between the channels igniting with the deflector plate 17 a narrow slit or duct Formed in the flanged riser block 20 are a pair of grooves 29 and 30 positioned above and in communication with the channels 25 and 26, respectively. Groove 29 and channel 25 form an inlet chamber 31 while groove 30 and channel 26 form an expansion chamber or resonato'r chamber 32, both chambers being approximately the same size and configuration. A threaded inlet conduit 33 is formed in flanged riser block 20 at a right angle to the groove 29 for connection to a source of powder cloud. 1

An exhaust slot 34 is milled in the end of the plate 16 behind the entrance slot 23 and parallel to it. A flanged exhaust block 35 having a tubular element 36, closed by end plugs 37, secured to it, is fastened to the plate 16 by screws 21 so that the exhaust passage 38 in the flanged exhaust block 35 and the exhaust chamber 39 formed by tubular element 36 and plugs 37 are positioned directly' over the exhaust slot 34. Communicating with the exhaust chamber 39 is an exhaust conduit 40 inlug 41 secured to the tubular element 36, the exhaust conduit being connected by conduit or vacuum line 42 to a convenient form of dust collector 43 which may comprise a suction pump connected to a dust filter.

In operation, assume that the photoconductive insulating layer of the xerographic plate 10 bears an electrostatic latent image. The drive rolls 12, actuated by a power means (not shown) transport the carrier block 11, with the xerographic plate mounted thereon, relative to the development p ate .or electrode plate 15. A powder cloud generator or like sourceof developer material is then activated to supply a powder cloud of developer material to the xerographic plate via the entrance slot. 23 as the xerographic plate passes beneath the development plate. I

As shown in Fig. 1 the entrance slot 23 is supplied with a powder cloud by a conventional type powder cloud generator 44, such as those described in Hayford' Patent 2,812,883 and Andrus et al. Patent 2,815,330. The powder cloud, by whatever means produced, is then charged. Where a cloud of dry powdered developing material is used, any method of generating the cloud almost necessarily produces a charge thereon. For some purposes, the charge so produced is adequate. If it is desired to produce a more uniform charge, however, chargingdevice 45, such as triboelectric charging (as by passing the electroscopic powder through a narrow tube of suitable material in turbulent flow), corona charging or other charging device, may be used.

The charged powder cloud flows throughconduit 46 and elbow 47 threadedinto flanged riser block 20, and then it enters through inlet conduit 33 into the inlet chamber 31 where it fans out and flows through slit 28 and expansion chamber 32 and out entrance slot 23 past the knife edge of the deflector plate 17 (see Fig. 6), after which it jumps ditch 24. her, resonant flow occurs, and the periodicity of the vi-- brations in the expansion chamber is such that any powder agglomerates in the powder cloud are dispersed. If any.

agglomerates do pass through the expansion chamber without being separated, the powder cloud, as it leaves. the entrance slot flows over the sharp projected edge. of groove 24 thereby causing further dissemination of powder agglomerates.

With the xerographic plate moving past the developingapparatus and therefore pastthe entrance slot, "a uniform amount of developer powder is evenly distributed over the entire surface of the xerographic plate, the flow of the powder cloud, containing the deagglomerated developer material, being substantially laminar and paral lel to the xerographic plate in its passage through the development zone. As the chargeddeveloper powder particles are carried through the development zone, they selectively deposit on the surface of the xerographic plate in accordance with and in conformity With the electrostatic latent image on the xerographic plate to yield a developed xerographic print. Thus the xerographic plate is selectively developed by powder particles being deposited on the plate solely as a result of electrical forces attracting the powder particles to the surface of the plate, and not indiscriminately by powder particles adhering to the plate as a result of mechanical forces, such as friction which would result from a powder par,-. ticle striking the plate as a result of air movement.

In the expansion cham-l No powder cloud should near a plate bearingan electrostatic image where there is no electrode because reversal development is effected by virtue of the bias field between the xerographic plate and the development electrode. Powder which would therefore develop a charged and exposed xerographic plate without an electrode present would be damaging to the sensitometric quality of the resultant dust image. Therefore, escaping powder must be disposed of before it can deposit on a charged surface of a xerographic plate. This powder if not caught, causes peculiar reversed reversal effects, whereby powder is deposited in areas that should be free of powder.

In the embodiment disclosed, the development plate is substantially longer than the xerographic plate 10. With such an arrangement, only one exhaust slot 34 posi tioned behind the entrance slot 23 is required to remove excess powder particles flowing back from the entrance slot, the powder particles being drawn through the exhaust slot 34 connected to the source of negative pressure, dust collector 43. Downstream of the entrance slot, the powder particles are completely used up before they can exit from the development zone due to the length of the developing apparatus. Where a long xerographic plate is used with a relatively short electrode plate, escaping powder may be disposed of by placing a second exhaust slot at the opposite end of the electrode plate 16 from exhaust slot 34 in a manner similar to that disclosed in Carlson 2,842,456, issued July 8, 1958. The resultant dust images, developed by the use of the subject developing apparatus, are uniformly developed end-to-end, the images. being clearly and well defined with even grain due to the absence of agglomerates.

The xerographic plate and the development plate may be in the shape of flat members, asshown, or, if desired, they maybe curved to fit the contour of a drum for continuous operation. Although not shown, it is obvious that the development apparatus may be positioned within an enclosure to prevent loss of developer powder to external areas or merely to improve the appearance of the apparatus and in the case where a light-sensitive xerographic plate is used the enclosure may be made light-tight.

While there have been shown and described fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is moved in closely spaced relationship to the developing apparatus, said developing apparatus including an electrically conductive development plate, having an inclined entrance slot in saidv development plate located near one end of said development plate and extending transversely thereof; an expansion chamber, a duct, an inlet chamber and an inlet conduit in said development plate; said inlet conduit, said inlet chamber, and said duct being connected inseries toeach other, said expansionchamber being connected to said duct intermediate said inlet chamber and said inclined entrance slot; said inlet conduit being connectable to a source of powdered developing material,

whereby a cloud of developing material can be flowed throughsaid entrance slot in a laminar flow parallel to the surface of a xerographic plate, anexhaust slot -insaid developme nt plate positioned betweensaid inclined entrance slot and an end of said development plate away.

fi'om' the laminar fiow..pa th..ofja,cloud ofdevelpper.

material leaving 'saidflincl'ined emr'anceis st, an exhaust,

6 conduit means in said development plate connected at one end to said exhaust slot and being conn'ectable at its other end to a vacuum line. I

2. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electro static latent image is positioned in closely spaced relationship to the developing apparatus for development by a powdered developing material, said developing apparatus including an electrically conductive electrode plate having a surface portion conformable with the surface of the xerographic plate, a conduit means for powdered developing material in said electrode plate, said powdered developing conduit means including an entrance slot extending transversely of said electrode plate, said entrance slot forming an angle of approximately two degrees with said surface of said electrode plate conformable with the surface of the xerographic plate, said powder cloud conduit means also including an expansion chamber, a duct and an inlet chamber, said inlet chamber and said duct being connected in series with each other, and said expansion chamber acting as a shunt connection between said duct and said entrance slot; said inlet chamber being connectable to a source of powder cloud development material; and exhaust means in said electrode plate, said exhaust means including an exhaust slot extending transversely of said electrode plate and parallel to said entrance slot with respect to the direction of fiow of a powder cloud development material from said entrance slot, and an outlet passage connectable to a vacuum line.

3. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced relationship to the developing apparatus for development by powdered developing material, said developing apparatus including an electrically conductive electrode plate having a surface portion conformable with the surface of the xerographic plate, a powdered developing material conduit means in said electrode plate, said powder cloud conduit means including an entrance slot extending transversely of said electrode plate, said entrance slot forming an angle of approximately two degrees with said surface of said electrode plate conformable with the surface of the xerographic plate, said powder cloud conduit means also including an expansion chamber, an inlet chamber and an inlet means, said inlet means being connected in series with said inlet chamber, and said expansion chamber being connected as a shunt betweensaid inlet chamber and said entrance slot, said inlet means being connectable to a source ofpowdered developing material, and an exhaust means in saidelectrode plate, said exhaust means including an exhaust slot extending transversely of said electrode plate and parallel to said entrance slot but behind said entrance slot With respect to the direction of flow of powdered developing material through said entrance slot, and an outlet passage connectable to a vacuum line.

4. A developing apparatus for use in the development station of a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is moved in closely spaced relationship to the developing apparatus, said developing apparatus including an electrically con ductive development plate having a surface conformable with the surface of the xerographic plate, an entrance slot in said development plate located near one end of said plate, an expansion chamber, a duct, an inlet chamber and an inlet conduit, in said development plate; said inlet conduit, said inlet chamber, and said duct being connected in series with said expansion chamber being connected to said duct intermediate said inlet chamber and said entrance slot; said inlet conduit being;

entrance slot and the end of said development plate away from said groove, an exhaust conduit means in said development plate connected at one end to said exhaust slot and being connectable at its other end to a vacuum line'whereby excess development material may be removed from the development station of the xerographic machine.

5. A'developing'apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is closely spaced to the developing ap paratus, said developing apparatus including an electrically conductive development plate, an entrance slot in said development plate extending transversely of and at one end of said development plate, an expansion chamber and an inlet chamber in said development plate connected to said entrance slot, said expansion chamber being connected in parallel between'said inlet chamber and said entrance slot, .said inlet chamber being connectable to a source of powder cloud development material for flowing a powdered developing material through said entrance slot over the xerographic plate as it moves relative to the development electrode, an exhaust slot in and at said one end of said development plate extending parallel to said entrance slot and between said'entrance slot and said one end of said development plate, and conduit means in said development plate connected at one end to said exhaust slot and being connectable at its other end to a vacuum line.

6. A developing apparatus for use in a xerographic machine wherein a'xerographic plate carrying an electrostatic latent image is positioned in closely spaced relationship to the developing apparatus for development by powdered developing material, said developing apparatus including an electrode plate, having a powder cloud conduit means in said electrode plate, said powder cloud conduit means including an entrance slot extending transversely of'said electrode plate, an expansion chamber, a duct, an inlet chamber and an inlet conduit, said inlet conduit, said inlet chamber and said duct being connected in series and said expansion chamber being connected in parallel to said duct and said entrance slot; said inlet conduit being connectable to a source of powder cloud development material, and at least one exhaust means in said electrode plate, said exhaust means including an exhaust slot extending transversely of said electrode plate and parallel to said entrance slot and an exhaust conduit, said exhaust conduit being connectable to a vacuum line.

7. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced relationship to the developing apparatus, said developing apparatus including an electrically conductive electrode plate having a surface conformable with the surface of the xerographic plate, a groove, an entrance slot and an exhaust slot in said electrode plate, extending transversely of and at one end of said electrode plate parallel to each other, said entrance slot being positioned at an angle of approximately two degrees to said surface of said plate to permit flow of developing material over said groove, conduit means in said electrode plate connected to said entrance slot,'said conduit means including an expansion chamber and an inlet chamber, said inlet chamber being connectable at one end to a source of powdered developing material and being connected at its opposite end to said entrance chamber by means of said expansion chamber whereby the powdered developing material may flow through said inlet chamber, said expansion chamberand then through said entrance slot and out across said groove,- and exhaust conduit means in said electrode plate connected at one end to said exhaust slot and connectable at its opposite end to a vacuum line. 7

8. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is moved in closely spaced relation to the'developing apparatus, said developing apparatus including an electrically conductive development plate, having an entrance slot in said development plate located near one end of said development plate; an expansion chamber, a duct, an inlet chamber in said development plate; said inlet chamber, said, duct and said expansion chamber being connected in sequence to said entrance slot; and an inlet conduit connectable to a source of powdered developing material connected to said inlet chamber whereby powdered developing material can be flowed through said inlet chamber through said duct into said expansion chamber from whence it may flow through said entrance slot into laminar flow parallel to the surface of a xerographic plate.

y 9. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced relationship to the developing apparatus for development by develop ing material, said developing apparatus including an elec trically conductive electrode plate having a surface con formable with the surface of the xerographic plate, a conduit means for powder cloud developing material in said electrode plate, said powder cloud conduit means including an entrance slot extending transversely of said electrode plate, said entrance slot forming an angle of approximately two degrees with said surface of' said electrode' plate conformable with the surface of the xerographic plate, and said powder cloud conduit means also including an expansion chamber, connecting means, and an inlet chamber of approximately equal size connected to said entrance slot with said expansion chamber connected in parallel to said inlet chamber between said inlet chamber and said entrance slot by said connecting means, said inlet chamber being connectable to a source of powder cloud development material.

10. A developing apparatus for use in the development station of a xerographic machine wherein a fiat xerographic plate carrying an electrostatic latent image is moved past and in closely spaced relationship to the developing apparatus, said developing apparatus including an electrically conductive development plate having a surface conformable with the surface of the xerographic plate, an entrance slot in said development plate extending transversely thereof and located near one end of said development plate, anexpansion chamber, a connecting means, an inlet chamber of the same size and configuration as said expansion chamber and an inlet conduit in said development plate; said inlet conduit, said'inlet chamber, and said connecting means being connected in series to each other, said expansion chamber connecting said connecting means to said entrance slot; said inlet conduit being connectable to a source of powdered developing material whereby a cloud of powdered developing material can be flowed through said entrance slot in laminar flow substantially parallel to the surface of the xerographic plate, and a groove in said surface of said development plate positioned so that the flow of develop-' ing material from said entrance slot passes said groove laterally.

11. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced relationship to the developing apparatus, said developing apparatus including an electrically conductive electrode plate having a surface conformable with the surface of a xerographic plate, a groove, an entrance slot and an exhaust slot in said electrode plate, extending transversely of and at one end of said electrode plate parallel to each other, said entrance slot being positioned at an angle of approximately two degrees to said surface of said plate,

and conduit means in said electrode plate connected to said entrance slot, said conduit means including an expansion chamber and an inlet chamber of approximately the same size and configuration connected in parallel to said entrance slot, said inlet chamber being connectable to a source of powdered developing material whereby the powdered developing material may flow through said inlet chamber, said expansion chamber and then through said entrance slot and across said groove whereby the xerographic plate is selectively developed by the powdered developing material being deposited on the xerographic plate solely as a result of electrical forces attracting the powdered developing material to the surface of a xerographic plate, said exhaust slot being connectable to a vacuum source whereby excess powdered developing material not deposited on the surface of a xerographic plate may be removed through said exhaust slot.

12. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced movable relation to the developing apparatus for development by developing material, said developing apparatus including a plate of conductive material, said plate having a beveled undercut portion in a face of said plate, a tapered deflector plate secured in said beveled undercut portion of said plate defining with said plate an entrance slot at an angle of approximately two degrees with said face of said plate, said plate having an expansion chamber connected to said entrance slot, a connecting means, and an inlet chamber of approximately the same size and configuration as said expansion chamber, said connecting means connecting said expansion chamber to said inlet chamber, and said inlet chamber being connectable to a source of developing material.

13. A development electrode for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is moved in closely spaced relation with respect to the development electrode for development by an aerosol of developing material, said development electrode including an electrically conductive electrode plate having a surface portion conformable with the surface of a xerographic plate, an entrance slot, a resonator chamber, a duct, and an inlet chamber in said electrode plate, said entrance slot extending transversely of said electrode plate forming an angle of approximately two degrees with said surface of said electrode plate conformable with the surface of a xerographic plate, said resonator chamber having approximately the same configuration as said inlet chamber and approximately the same size, the volume of both the resonator chamber and the inlet chamber being greater than the volume of either said entrance slot or said duct, said inlet chamber being connected at one end to one end of said duct and at its other end to a source of an aerosol of developing material, the other end of said duct being connected to one end of said resonator chamber to which is also connected one end of said entrance slot, whereby an aerosol of developing material entering said inlet chamber expands therein before flowing out through said duct into said resonator chamber, from whence it fiows out through said entrance duct, resonant fiow occurring in the resonator chamber to disperse any agglomerates which may be present in the developing material.

Hayford Oct. 1, 1957 Carlson July 8, 1958 

